Hi Remi,
We are members of the Experimental Aircraft Association who have
built an 'experimental aircraft'. As such, among other things not
included in our standard kit, we have installed a mixture control on our
912S which bleeds manifold pressure back into the carb bowl vents.
Testing has shown that the standard rotax carb settings are actually
lean-of-peak at sea level on the front two cylinders and that it (of
course) gets richer with altitude, passing thru peak and on down the
richer side of peak EGT with increasing altitude. It is our assumption
that it is acceptable for them to run the engines this way (lean of peak
at take off) because the heads are liquid cooled.
We believe it is then a fair assumption that we can run the engine
lean-of-peak at altitude and <75% power, given that the factory settings
run the engine lean-of-peak at full power/sea level. Of course we
monitor our exhaust, head, water, and oil temps just to make sure
everything is happy while leaning at altitude.
regards,
Terry Seaver
A135/N135TD
Monowheel XS, 912S, Airmaster prop
________________________________
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Remi
Guerner
Sent: Friday, December 26, 2008 11:53 AM
Subject: Europa-List: Mixture control
Ron,
You will be adding a complicated system to an already complicated
engine. I am afraid this will further reduce the reliability of your
engine. Dealing with this sort of experiment on the ground (I mean on a
car or a motorbike) is something. Doing it on an airplane is another
story, especially if you want to use your bird as a reasonably reliable
cross country machine.
Just my personal opinion.
Regards
Remi
>>>>>>>>>>>N4211W not flying yet, but have and will install a mixture
control on 914.
First off installed will be a Split Second mixture display that is
driven
by a Bosch O2 sensor (will weld a bung on the muffler inlet just
downstream of turbo).
Slight different install on 914 because of Turbo compared to 912/s, but
will use a needle valve to leak pressure from normal airbox pressure
side
of enrichment solenoid to manifold cross tube. The more I leak the
leaner
the mixture will be.
This will require a run of hose to cockpit then to manifold cross tube,
I
will use high temperature Viton tubing.
I will slight richen mixture on main jet and perhaps even jet needle, I
always like to run slight rich when you are making a lot of BTUs such as
100% power or in 914s case War emergency of 115%. It can also cool
things
a little on a hot engine (including when stuck on ground).
Then will size a restriction on the controlled "leak" to manifold cross
tube so it will allow me to only lean to ~14.7 at 18K.
Then will have an emergency "rich" button that will allow me to activate
enrichment solenoid that could further richen mixture on less than War
emergency power if I wish. In addition the emergency "rich" button will
completely bypass all my additional plumbing.
For either a 912/S or 914 install, if you at cruise power if you pull
throttle without closing off your controlled leak, your engine is
probably
going to quit. On the other hand, if you set mixture at lets say 60%
power
and adjust mixture, if you increase power you will go richer than
probably
desired.
Another problem is if you lean at altitude, when you come down things
will
lean up further.
Having a Split Second display is a nice tool for this control, a EGT
(which I have one on each side of motor) is only semi useful.
HAC has or had a altitude adjusting bellows, I would rather have full
manual control.
I am a motorhead and feel very comfortable fiddling with carburation. If
you can't tune a lawnmower engine to perfection by ear, owned a hot 2
stroke cycle that you managed to run on the edge for long periods
without
blowing up, probably not worth considering the controlled 'leak' method
of
adjusting Type 64 constant depression carbs.
Ron P.>>>>>>>>>>>>
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